The present invention relates to detergent particles and a process for producing the particles. More particularly, the present invention relates to a process for producing coated detergent particles.
Recently, there has been considerable interest within the detergent industry for laundry detergents which have the convenience, aesthetics and solubility of liquid laundry detergent products, but retain the cleaning performance and cost of granular detergent products. The problems, however, associated with past granular detergent compositions with regard to aesthetics, solubility and user convenience are formidable. Such problems have been exacerbated by the advent of xe2x80x9ccompactxe2x80x9d or low dosage granular detergent products which typically do not dissolve in washing solutions as well as their liquid laundry detergent counterparts. These low dosage detergents are currently in high demand as they conserve resources and can be sold in small packages which are more convenient for consumers prior to use, but less convenient upon dispensing into the washing machine as compared to liquid laundry detergent which can be simply poured directly from the bottle as opposed to xe2x80x9cscoopedxe2x80x9d from the box and then dispensed into the washing solution.
As mentioned, such low dosage or xe2x80x9ccompactxe2x80x9d detergent products unfortunately experience dissolution problems, especially in cold temperature laundering solutions (i.e., less than about 30xc2x0 C.). More specifically, poor dissolution results in the formation of xe2x80x9cclumpsxe2x80x9d which appear as solid white masses remaining in the washing machine or on the laundered clothes after conventional washing cycles. These xe2x80x9cclumpsxe2x80x9d are especially prevalent under cold temperature washing conditions and/or when the order of addition to the washing machine is laundry detergent first, clothes second and water last (commonly known as the xe2x80x9cReverse Order Of Additionxe2x80x9d or xe2x80x9cROOAxe2x80x9d). Such undesirable xe2x80x9cclumpsxe2x80x9d are also formed if the consumer loads the washing machine in the order of clothes, detergent and then water. Similarly, this clumping phenomenon can contribute to the incomplete dispensing of detergent in washing machines equipped with dispenser drawers or in other dispensing devices, such as a granulette. In this case, the undesired result is undissolved detergent residue in the dispensing device.
It has been found that the cause of the aforementioned dissolution problem is associated with the xe2x80x9cbridgingxe2x80x9d of a xe2x80x9cgel-likexe2x80x9d substance between surfactant-containing particles to form undesirable xe2x80x9cclumps.xe2x80x9d The gel-like substance responsible for the undesirable xe2x80x9cbridgingxe2x80x9d of particles into xe2x80x9cclumpsxe2x80x9d originates from the partial dissolution of surfactant in the aqueous laundering solutions, wherein such partial dissolution causes the formation of a viscous surfactant phase or paste which binds or otherwise xe2x80x9cbridgesxe2x80x9d other surfactant-containing particles together into xe2x80x9cclumps.xe2x80x9d This undesirable dissolution phenomena is commonly referred to as xe2x80x9clump-gelxe2x80x9d formation. In addition to the viscous surfactant xe2x80x9cbridgingxe2x80x9d effect, inorganic salts have a tendency to hydrate which can also cause xe2x80x9cbridgingxe2x80x9d of particles which linked together via hydration. In particular, inorganic salts hydrate with one another to form a cage structure which exhibits poor dissolution and ultimately ends up as a xe2x80x9cclumpxe2x80x9d after the washing cycle. It would therefore be desirable to have a detergent composition which does not experience the dissolution problems identified above so as to result in improved cleaning performance.
The prior art is replete with disclosures addressing the dissolution problems associated with granular detergent compositions. For example, the prior art suggests limiting the use and manner of inorganic salts which can cause clumps via the xe2x80x9cbridgingxe2x80x9d of hydrated salts during the laundering cycle. Specific ratios of selected inorganic salts are contemplated so as to minimize dissolution problems. Such a solution, however, constricts the formulation and process flexibility which are necessary for current commercialization of large-scale detergent products. Various other mechanisms have been suggested by the prior art, all of which involve formulation alteration, and thereby reduce formulation flexibility. As a consequence, it would therefore be desirable to have a process by which detergent compositions having improved dissolution without significantly inhibiting formulation flexibility can be produced.
Accordingly, the need remains for a process which can produce a detergent granule having improved flow properties and aesthetics, as well as improved solubility, which may be included in detergent compositions.
This need is met by the present invention wherein a process for producing a detergent particle that has improved surface, appearance, flow properties, and improved solubility is provided. The particles of the present invention have improved surface properties in that they are smoother and have a generally more uniform surface and appearance than prior art detergent particles. Further, the appearance of the particles have been improved in that they appear brighter and whiter than currently available detergent particles and have improved flow properties where the particles have reduced lumping and caking profiles.
In accordance with the present invention, a process for preparing detergent compositions including granules having a coating layer of a water-soluble material is provided. The process comprises providing detergent granules having at least one detergent active material and passing those detergent granules through a coating mixer such as a low speed mixer or fluid bed mixer and coating the particle core with a coating solution or slurry of the water soluble coating material. Upon drying, the resultant detergent particles have improved appearance and flow properties and may be packaged and sold as a detergent material or mixed with various other detergent ingredients to provide a fully formulated detergent composition.
The water soluble coating material is selected from the group consisting of detersive surfactants such as anionic surfactants, hydrotropes such as sulfonates, polyethylene glycols and polypropylene glycols and mixtures thereof. In preferred embodiments, the coating material is a mixture of an anionic surfactant and a hydrotrope in a ratio of anionic surfactant to hydrotrope of from about 95:5 to about 5:95. Particularly preferred are (a) a mixture of sodium linear alkyl benzene sulfonate, hydrophobic secondary alkyl sulfate, and/or sodium xylene sulfonate or (b) a mixture of sodium linear alkyl benzene sulfonate, hydrophobic secondary alkyl sulfate, and/or disodium alkyldiphenyloxide disulfonate (commercially known as Dowfax hydrotrope with the alkyl group having a chainlength from C1-C10), at a ratio of surfactants to hydrotrope of from about 70:30 to about 95:5. Preferably, the amount of water-soluble solution is from about 1% to about 30%, by weight, of the detergent composition. Alternatively, coating material and thus the particle coating layer may also include detergent adjunct ingredients such as brighteners, chelants, nonionic surfactants, co-builders, etc incorporated into the coating.
In an optional embodiment of the present process, the process further comprises the steps of mixing the coated detergent granules with a flow control aid to adhere the flow control aid to the surface of the granules. The flow control aid is preferably an inorganic powder material with a mean particle size of less than about 100 microns and is selected from the group consisting of crystalline layered silicate, carbonate, sodium sulfate, aluminosilicate, magnesium silicate, calcium silicate, clay, and mixtures thereof.
Accordingly, it is an object of the present invention to provide a process for producing a detergent composition having improved appearance and flow characteristics by coating detergent granules with a layer of a water soluble materials. It is a further object of the present invention to provide a process for preparing the detergent particle via coating in a mixer with solutions or slurries of the inorganic materials. These and other objects features and advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description and the appended claims.